It is frequently important to measure or sense an angular displacement and/or relative torque between two shafts. The relative displacement can be measured by a small angle displacement sensor. The relative displacement can then be used to derive the torque applied between the two shafts.
For example, power steering systems in motor vehicles, etc. are designed to provide appropriate hydraulic or electrical assist to allow a driver to complete a turn of the motor vehicle. The driver usually turns a steering wheel that is connected to a first shaft. The first shaft is coupled to a second shaft that is connected to a steering mechanism. The first and second shafts can be coupled together by a compliant member, such as a torsion bar. The first shaft can rotate with respect to the second shaft by a predetermined number of degrees, e.g., ±12 degrees. Mechanical stops can prevent further movement. The amount of assist is determined as a function of the amount of torque being applied to the first shaft.
Many types of position sensors require a ring magnet to be pressed onto a shaft. Unfortunately, the magnetic rings of such position sensors are composed of a brittle magnetic material that can crack during assembly. This assembly is particularly stressful to the magnetic material because it involves forcing each magnetic ring onto a shaft. The inner diameter of each magnetic ring is sized to fit tightly around the shaft to prevent it from sliding along the shaft. Unfortunately, attaching the magnetic ring to the shaft in this manner imparts hoop stresses on the magnetic ring that can cause it to fracture.
It is therefore desirable to develop an improved device for attaching the magnetic ring to the shaft of the rotor assembly without causing it to fracture.